Light-emitting device

ABSTRACT

A light-emitting device of an embodiment of the present disclosure comprises a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer, wherein the first type semiconductor layer comprises a non-planar roughened surface; a bonding layer formed between the substrate and the semiconductor stack; and multiple recesses each comprising a bottom surface lower than the non-planar roughened surface; and multiple buried electrodes physically buried in the first type semiconductor layer, wherein the multiple buried electrodes are formed in the multiple recesses respectively, and one of the multiple buried electrodes comprises an upper surface higher than the non-planar roughened surface of the first type semiconductor layer.

REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/421,898 entitled “LIGHT-EMITTING DEVICE”, filed on Mar. 16,2012, the contents of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The application relates to a light-emitting device, and moreparticularly, to a light-emitting device with a plurality of buriedelectrodes.

DESCRIPTION OF BACKGROUND ART

The light-emitting diode (LED) is a solid state semiconductor device,which has been broadly used as a light-emitting device. Thelight-emitting device structure comprises a p-type semiconductor layer,an n-type semiconductor layer, and an active layer. The active layer isformed between the p-type semiconductor layer and the n-typesemiconductor layer. The structure of the light-emitting devicegenerally comprises III-V group compound semiconductor such as galliumphosphide, gallium arsenide, or gallium nitride. The light-emittingprinciple of the LED is the transformation of electrical energy tooptical energy by applying electrical current to the p-n junction togenerate electrons and holes. Then, the LED emits light when theelectrons and the holes combine.

FIG. 1A illustrates a conventional light-emitting device 1 a. Thelight-emitting device 1 a comprises a substrate 15 a; a semiconductorstack 10 a comprising a first type semiconductor layer 13 a, a secondtype semiconductor layer 11 a and an active layer 12 a formed betweenthe first type semiconductor layer 13 a and the second typesemiconductor layer 11 a; a first electrode 18 a electrically connectedto the first type semiconductor layer 13 a; and a second electrode 19 aelectrically connected to the second type semiconductor layer 11 a. Thematerial of the first electrode 18 a and the second electrode 19 acomprises metal or metal alloy. As illustrated in FIG. 1A, the firstelectrode 18 a is formed on a top surface 17 a of the light-emittingdevice 1 a. The electrical current from the first electrode 18 a is notdispersed uniformly in the first type semiconductor layer 13 a of thelight-emitting device 1 a.

FIG. 1B illustrates another example of a conventional light-emittingdevice 1 b. The light-emitting device 1 b comprises a substrate 15 b; asemiconductor stack 10 b comprising a first type semiconductor layer 13b, a second type semiconductor layer 11 b and an active layer 12 bformed between the first type semiconductor layer 13 b and the secondtype semiconductor layer 11 b; a first electrode 18 b electricallyconnected to the first type semiconductor layer 13 b; a second electrode19 b electrically connected to the second type semiconductor layer 11 b;and a conductive layer 16 b formed between the first type semiconductorlayer 13 b and the first electrode 18 b. The material of the firstelectrode 18 b and the second electrode 19 b comprises metal or metalalloy.

As illustrated in FIG. 1B, the conductive layer 16 b is formed on thefirst type semiconductor layer 13 b and the first electrode 18 b isformed on a top surface 17 b of the conductive layer 16 b. The materialof the conductive layer 16 b comprises thin metal or metal alloy. Theconductive layer 16 b is used to improve the electrical currentspreading. However, the transmittance of the conductive layer 16 b islow, and the light emitting efficiency of the light-emitting device 1 bis affected.

SUMMARY OF THE DISCLOSURE

A light-emitting device of an embodiment of the present disclosurecomprises a substrate; a semiconductor stack comprising a first typesemiconductor layer, a second type semiconductor layer and an activelayer formed between the first type semiconductor layer and the secondtype semiconductor layer, wherein the first type semiconductor layercomprises a non-planar roughened surface; a bonding layer formed betweenthe substrate and the semiconductor stack; and multiple recesses eachcomprising a bottom surface lower than the non-planar roughened surface;and multiple buried electrodes physically buried in the first typesemiconductor layer, wherein the multiple buried electrodes are formedin the multiple recesses respectively, and one of the multiple buriedelectrodes comprises an upper surface higher than the non-planarroughened surface of the first type semiconductor layer.

A light-emitting device of an embodiment of the present disclosurecomprises a substrate; a semiconductor stack comprising a first typesemiconductor layer, a second type semiconductor layer and an activelayer formed between the first type semiconductor layer and the secondtype semiconductor layer wherein the first type semiconductor layercomprises a top surface; a bonding layer formed between the substrateand the semiconductor stack; multiple recesses recessed from the topsurface toward the active layer; and multiple buried electrodes in themultiple recesses respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional diagram of a conventionallight-emitting device;

FIG. 1B illustrates a cross-sectional diagram of a conventionallight-emitting device;

FIG. 2 illustrates a cross-sectional diagram of a light-emitting deviceaccording to the first embodiment of the present disclosure;

FIGS. 3A to 3D illustrate a process flow for manufacturing thelight-emitting device according to an embodiment of the presentdisclosure;

FIGS. 4A to 4C illustrate cross-sectional diagrams of a plurality ofburied electrodes in a light-emitting device according to the firstembodiment of the present disclosure;

FIGS. 5A to 5I illustrate cross-sectional diagrams of a plurality ofburied electrodes in a light-emitting device according to the firstembodiment of the present disclosure;

FIG. 6 illustrates a cross-sectional diagram of a light-emitting deviceaccording to the second embodiment of the present disclosure;

FIGS. 7A to 7B illustrate cross-sectional diagrams of a plurality ofburied electrodes in a light-emitting device according to the secondembodiment of the present disclosure;

FIG. 8 illustrates a cross-sectional diagram of a light-emitting deviceaccording to the third embodiment of the present disclosure; and

FIGS. 9A to 9B illustrate cross-sectional diagrams of a plurality ofburied electrodes in a light-emitting device according to the thirdembodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiment of the disclosure is illustrated in detail, and isplotted in the drawings. The same or the similar part is illustrated inthe drawings and the specification with the same number.

FIG. 2 illustrates a cross-sectional diagram of a light-emitting device2 according to the first embodiment of the present disclosure. Thelight-emitting device 2 comprises a substrate 27; a semiconductor stack20 comprising a first type semiconductor layer 23, a second typesemiconductor layer 21 and an active layer 22 formed between the firsttype semiconductor layer 23 and the second type semiconductor layer 21;a bonding layer 25 formed between the substrate 27 and the semiconductorstack 20; a first electrode 28 electrically connected to the first typesemiconductor layer 23; a second electrode 29 electrically connected tothe second type semiconductor layer 21; and a plurality of buriedelectrodes 24 physically buried in the first type semiconductor layer 23and electrically connected to the first electrode 28.

The material of the semiconductor stack 20 comprises III-V group basedsemiconductor material such as InGaN, AlGaAs, or AlGaInP. Thesemiconductor stack 20 is epitaxially grown on a growth substrate (notshown). The method of forming each layer of the semiconductor stack 20is not particularly limited. Besides a metal organic chemical vapordeposition method (MOCVD method), each layer of the semiconductor stack20 may be formed by a known method such as a molecular beam epitaxymethod (MBE method), a hydride vapor phase epitaxy method (HVPE method),a sputtering method, an ion-plating method and an electron showeringmethod.

The plurality of buried electrodes 24 buried in the first typesemiconductor layer 23 increases the contact area between the buriedelectrode 24 and the first type semiconductor layer 23. Each of theplurality of the buried electrode 24 electrically connected to eachother with an extension electrode (not shown). With the buried electrode24, the contact area between the buried electrode 24 and the first typesemiconductor layer 23 is increased and an electrical current isinjected into the first type semiconductor layer 23 uniformly.

A trench 200 is formed in the semiconductor stack 20 by etching process.A sidewall 200 a of the trench 200 is insulated from the semiconductorstack 20 with dielectric materials such as SiO₂ and Si₃N₄. A conductivechannel is formed by filling conductive material in the trench 200,wherein the conductive material can be metal or metal alloy, or atransparent conductive material like ITO or ZnO. The materials of theplurality of buried electrodes 24 and the first electrode 28 compriseconductive materials such as metal or metal alloy, and transparentconductive materials such as ITO or ZnO. The materials of the pluralityof buried electrodes 24, the first electrode 28 and the trench 200 arethe same or different from each other. The plurality of buriedelectrodes 24 and the first electrode 28 are electrically connected viathe conductive channel. The first electrode 28 and the second electrode29 are formed on the same side of the semiconductor stack 20 opposite toa top surface 23 a of the first type semiconductor layer 23. The firstelectrode 28 and the second electrode 29 are isolated from each other byan isolation layer 200 b. The material of the isolation layer 200 bcomprises dielectric material such as SiO₂ and Si₃N₄.

As shown in FIG. 2, the substrate 27 is a transparent substrate. A lightemitted from the active layer 22 can be emitted out through thetransparent substrate 27. The material of the substrate 27 can besapphire, glass, GaP, ZnSe and SiC. The substrate 27 is attached to thefirst type semiconductor layer 23 by the bonding layer 25. The materialof the bonding layer 25 can be transparent material such as epoxy,polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB),spin-on glass (SOG) and silicone.

When the light-emitting device 2 is operated under a high electricalcurrent, the thickness of the buried electrode 24 is preferred to bethick with a range of about 2˜6 μm to reduce the sheet resistance of thelight-emitting device 2 and increase the device reliability. As shown inFIG. 2, when the light emitted from the active layer 22 passes throughthe bonding layer 25, part of the light is absorbed by the bonding layer25. In order to reduce the thickness H2 a of the bonding layer 25,improve the light emission efficiency of the light-emitting device 2 andmaintain the thickness of the buried electrode 24 in a range of about2˜6 μm, the plurality of buried electrodes 24 is buried in the firsttype semiconductor layer 23. The first type semiconductor layer 23comprises the top surface 23 a and a plurality of recesses 24 a. Each ofthe plurality of recesses 24 a comprises a bottom surface 24 b lowerthan the top surface 23 a of the first type semiconductor layer 23. Theconductive materials such as metal or metal alloy, or the transparentconductive materials such as ITO or ZnO are formed in the plurality ofrecesses 24 a to form the plurality of buried electrodes 24. Theconductive materials or the transparent conductive materials can beformed in the plurality of recesses 24 a by electron beam evaporation,physical vapor deposition or sputter deposition.

FIGS. 3A-3D illustrate a process flow for manufacturing a light-emittingdevice 3 according to an embodiment of the present disclosure. As shownin FIGS. 3A-3D, a photoresist layer 31 formed on a top surface 35 of asemiconductor stack 30 is used to define the pattern of a plurality ofburied electrodes 34 of the light-emitting device 3 by a conventionallithography process. As shown in FIG. 3B, a plurality of recesses 37 isformed by etching the semiconductor stack 30 through an area 32 notprotected by the photoresist layer 31. A depth D2 of each of theplurality of recesses 37 is controlled by dry etching process parameterssuch as etch time, etchant gas flow rate and etchant gas type. A wetetch process is optionally performed to clean the surface containmentsof the plurality of recesses 37, and flatten a sidewall surface 37 s anda bottom surface 37 b of each of the plurality of recesses 37. As shownin FIG. 3C, a conductive material 33 is formed in the plurality ofrecesses 37 and on a top surface 36 of the photoresist layer 31. Theadhesion between the semiconductor stack 30 and the conductive material33 is improved because of the flat sidewall surface 37 s and bottomsurface 37 b of each of the plurality of recesses 37. As shown in FIG.3D, the photoresist layer 31 is lifted off by the conventional etchmethod and the plurality of buried electrodes 34 is buried in thesemiconductor stack 30. The thickness T3 of each of the plurality ofburied electrodes 34 is controlled by thin-film deposition process suchas deposition rate and deposition time. After the pattern definitionprocess and the deposition process as shown in FIGS. 3A-3D are finished,the plurality of buried electrodes 34 comprising an upper surface 341 isformed in the plurality of recesses 37 correspondingly.

As shown in FIG. 2, the plurality of buried electrodes 24 is buried inthe first type semiconductor layer 23 by the method illustrated in FIGS.3A-3D. Each of the plurality of buried electrodes 24 comprises anembedded portion 242 formed under the top surface 23 a of the first typesemiconductor layer 23 and an exposed portion 241 formed above the topsurface 23 a of the first type semiconductor layer 23. The embeddedportion 242 is physically buried in the first type semiconductor layer23 and electrically connected to the first type semiconductor layer 23.The thickness H2 of the exposed portion of each of the plurality ofburied electrodes 24 is reduced compared with that of the electrode notburied in the first type semiconductor layer. Because the thickness H2of the exposed portion of each of the plurality of buried electrodes 24is reduced, the thickness H2 a of the bonding layer 25 used to attachthe substrate 27 to the semiconductor stack 20 is also reduced.

The thickness H2 a of the bonding layer 25 is related with the thicknessH2 of the exposed portion 241 of each of the plurality of buriedelectrodes 24. As the thickness H2 of the exposed portion 241 isincreased, the thickness H2 a of the bonding layer 25 is preferred to beincreased to provide adhesion between the substrate 27 and thesemiconductor stack 20. FIGS. 4A-4C illustrate different examples of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure.

FIG. 4A illustrates an example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. As shown inFIG. 4A, an upper surface 443 of each of the plurality of buriedelectrodes 24 is higher than the top surface 23 a of the first typesemiconductor layer 23. Each of the plurality of buried electrodes 24comprises the embedded portion 242 formed under the top surface 23 a ofthe first type semiconductor layer 23 and the exposed portion 241 formedabove the top surface 23 a of the first type semiconductor layer 23. Thesize of the embedded portion 242 is smaller than that of the exposedportion 241.

FIG. 4B illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The size ofthe embedded portion 242 is equal to that of the exposed portion 241.

FIG. 4C illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The size ofthe embedded portion 242 is larger than that of the exposed portion 241.

As shown in FIG. 2, in order to increase the light emission efficiencyof the light-emitting device 2, the top surface 23 a of the first typesemiconductor layer 23 can be a non-planar surface such as the one ofthe cross-sectional diagrams illustrated in FIGS. 5A-5I.

FIG. 5A illustrates an example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is a non-planarsurface. In the present embodiment, the non-planar surface is aroughened surface 23 a′, and an average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 illustrated in FIG. 2 is increased by theroughened surface 23 a′. As shown in FIG. 5A, the upper surface 443 ofeach of the plurality of buried electrodes 24 is higher than theroughened surface 23 a′ of the first type semiconductor layer 23. Eachof the plurality of buried electrodes 24 comprises the embedded portion242 formed under the top surface 23 a of the first type semiconductorlayer 23 and the exposed portion 241 formed above the top surface 23 aof the first type semiconductor layer 23. The embedded portion 242 isphysically buried in the first type semiconductor layer 23 andelectrically connected to the first type semiconductor layer 23. Thesize of the embedded portion 242 is smaller than that of the exposedportion 241.

FIG. 5B illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5B, the upper surface 443 of each of the plurality ofburied electrodes 24 is higher than the roughened surface 23 a′ of thefirst type semiconductor layer 23. Each of the plurality of buriedelectrodes 24 comprises the embedded portion 242 formed under the topsurface 23 a of the first type semiconductor layer 23 and the exposedportion 241 formed above the top surface 23 a of the first typesemiconductor layer 23. The embedded portion 242 is physically buried inthe first type semiconductor layer 23 and electrically connected to thefirst type semiconductor layer 23. The size of the embedded portion 242is equal to that of the exposed portion 241.

FIG. 5C illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the embodiment, the non-planar surface is the roughenedsurface 23 a′, and the average roughness of the roughened surface 23 a′is greater than 0.05 μm. The light emission efficiency of thelight-emitting device 2 is increased by the roughened surface 23 a′. Asshown in FIG. 5C, the upper surface 443 of each of the plurality ofburied electrodes 24 is higher than the roughened surface 23 a′ of thefirst type semiconductor layer 23. Each of the plurality of buriedelectrodes 24 comprises the embedded portion 242 formed under the topsurface 23 a of the first type semiconductor layer 23 and the exposedportion 241 formed above the top surface 23 a of the first typesemiconductor layer 23. The embedded portion 242 is physically buried inthe first type semiconductor layer 23 and electrically connected to thefirst type semiconductor layer 23. The size of the embedded portion 242is larger than that of the exposed portion 241.

When the top surface 23 a of the first type semiconductor layer 23 isthe roughened surface 23 a′ and the upper surface 443 of each of theplurality of buried electrodes 24 is higher than the roughened surface23 a′ of the first type semiconductor layer 23 as illustrated in FIGS.5A-5C, the thickness H2 a of the bonding layer 25 is determinedaccording to the thickness H2 of the exposed portion 241.

FIG. 5D illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5D, the upper surface 443 of each of the plurality ofburied electrodes 24 and the roughened surface 23 a′ of the first typesemiconductor layer 23 are substantially on the same plane. Each of theplurality of buried electrodes 24 comprises the embedded portion 242formed under the top surface 23 a of the first type semiconductor layer23 and the exposed portion 241 formed above the top surface 23 a of thefirst type semiconductor layer 23. The embedded portion 242 isphysically buried in the first type semiconductor layer 23 andelectrically connected to the first type semiconductor layer 23. Thesize of the embedded portion 242 is smaller than that of the exposedportion 241.

FIG. 5E illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present disclosure, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5E, the upper surface 443 of each of the plurality ofburied electrodes 24 and the roughened surface 23 a′ of the first typesemiconductor layer 23 are substantially on the same plane. Each of theplurality of buried electrodes 24 comprises the embedded portion 242formed under the top surface 23 a of the first type semiconductor layer23 and the exposed portion 241 formed above the top surface 23 a of thefirst type semiconductor layer 23. The embedded portion 242 isphysically buried in the first type semiconductor layer 23 andelectrically connected to the first type semiconductor layer 23. Thesize of the embedded portion 242 is larger than that of the exposedportion 241.

FIG. 5F illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5F, the upper surface 443 of each of the plurality ofburied electrodes 24 and the roughened surface 23 a′ of the first typesemiconductor layer 23 are substantially on the same plane. Each of theplurality of buried electrodes 24 comprises the embedded portion 242formed under the top surface 23 a of the first type semiconductor layer23 and the exposed portion 241 formed above the top surface 23 a of thefirst type semiconductor layer 23. The embedded portion 242 isphysically buried in the first type semiconductor layer 23 andelectrically connected to the first type semiconductor layer 23. Thesize of the embedded portion 242 is equal to that of the exposed portion241.

When the top surface 23 a of the first type semiconductor layer 23 isthe roughened surface 23 a′, and the upper surface 443 of each of theplurality of buried electrodes 24 and the roughened surface 23 a′ of thefirst type semiconductor layer 23 are substantially on the same plane asillustrated in FIGS. 5D-5F, the thickness H2 a of the bonding layer 25is preferred at least larger than 0.05 μm.

FIG. 5G illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5G, the upper surface 443 of each of the plurality ofburied electrodes 24 is lower than the roughened surface 23 a′ of thefirst type semiconductor layer 23. Each of the plurality of buriedelectrodes 24 comprises the embedded portion 242 formed under the topsurface 23 a of the first type semiconductor layer 23 and the exposedportion 241 formed above the top surface 23 a of the first typesemiconductor layer 23. The embedded portion 242 is physically buried inthe first type semiconductor layer 23 and electrically connected to thefirst type semiconductor layer 23. The size of the embedded portion 242is smaller than that of the exposed portion 241.

FIG. 5H illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5H, the upper surface 443 of each of the plurality ofburied electrodes 24 is lower than the roughened surface 23 a′ of thefirst type semiconductor layer 23. Each of the plurality of buriedelectrodes 24 comprises the embedded portion 242 formed under the topsurface 23 a of the first type semiconductor layer 23 and the exposedportion 241 formed above the top surface 23 a of the first typesemiconductor layer 23. The embedded portion 242 is physically buried inthe first type semiconductor layer 23 and electrically connected to thefirst type semiconductor layer 23. The size of the embedded portion 242is equal to that of the exposed portion 241.

FIG. 5I illustrates another example of a cross-sectional diagram of theplurality of buried electrodes 24 in the light-emitting device 2according to the first embodiment of the present disclosure. The topsurface 23 a of the first type semiconductor layer 23 is the non-planarsurface. In the present embodiment, the non-planar surface is theroughened surface 23 a′, and the average roughness of the roughenedsurface 23 a′ is greater than 0.05 μm. The light emission efficiency ofthe light-emitting device 2 is increased by the roughened surface 23 a′.As shown in FIG. 5I, the upper surface 443 of each of the plurality ofburied electrodes 24 is lower than the roughened surface 23 a′ of thefirst type semiconductor layer 23. Each of the plurality of buriedelectrodes 24 comprises the embedded portion 242 formed under the topsurface 23 a of the first type semiconductor layer 23 and the exposedportion 241 formed above the top surface 23 a of the first typesemiconductor layer 23. The embedded portion 242 is physically buried inthe first type semiconductor layer 23 and electrically connected to thefirst type semiconductor layer 23. The size of the embedded portion 242is larger than that of the exposed portion 241.

When the top surface 23 a of the first type semiconductor layer 23 isthe roughened surface 23 a′ and the upper surface 443 of each of theplurality of buried electrodes 24 is lower than the roughened surface 23a′ of the first type semiconductor layer 23 as illustrated in FIGS.5G-5I, the thickness H2 a of the bonding layer 25 is preferred at leastlarger than 0.05 μm.

FIG. 6 illustrates a cross-sectional diagram of a light-emitting device6 according to the second embodiment of the present disclosure. Thelight-emitting device 6 comprises a substrate 67; a semiconductor stack60 comprising a first type semiconductor layer 63, a second typesemiconductor layer 61, and an active layer 62 formed between the firsttype semiconductor layer 63 and the second type semiconductor layer 61;a bonding layer 65 formed between the substrate 67 and the semiconductorstack 60; a first electrode 68 electrically connected to the first typesemiconductor layer 63; a second electrode 69 electrically connected tothe second type semiconductor layer 61; and a plurality of buriedelectrodes 64 physically buried in the first type semiconductor layer 63and electrically connected to the first electrode 68.

The material of the semiconductor stack 60 comprises III-V group basedsemiconductor material such as InGaN, AlGaAs, or AlGaInP. Thesemiconductor stack 60 is epitaxially grown on a growth substrate (notshown). The method of forming each layer of the semiconductor stack 60is not particularly limited. Besides a metal organic chemical vapordeposition method (MOCVD method), each layer of the semiconductor stack60 may be formed by a known method such as a molecular beam epitaxymethod (MBE method), a hydride vapor phase epitaxy method (HVPE method),a sputtering method, an ion-plating method and an electron showeringmethod.

The plurality of buried electrodes 64 buried in the first typesemiconductor layer 63 increases the contact area between the buriedelectrode 64 and the first type semiconductor layer 63. Each of theplurality of the buried electrode 64 electrically connected to eachother with an extension electrode (not shown). With the buried electrode64, the contact area between the buried electrode 64 and the first typesemiconductor layer 63 is increased and an electrical current isinjected into the first type semiconductor layer 63 uniformly.

A trench 600 is formed in the semiconductor stack 60 by etching process.A sidewall 600 a of the trench 600 is insulated from the semiconductorstack 60 with dielectric materials such as SiO₂ or Si₃N₄. A conductivechannel is formed by filling conductive material in the trench 600,wherein the conductive material can be metal or metal alloy, or atransparent conductive material like ITO or ZnO. The materials of theplurality of buried electrodes 64 and the first electrode 68 compriseconductive materials such as metal or metal alloy, and transparentconductive materials such as ITO or ZnO. The materials of the pluralityof buried electrodes 64, the first electrode 68 and the trench 600 arethe same or different from each other. The plurality of buriedelectrodes 64 and the first electrode 68 are electrically connected viathe conductive channel. In the present embodiment, the first electrode68 and the second electrode 69 are formed on the same side of thesemiconductor stack 60 opposite to a top surface 63 a of the first typesemiconductor 63. The first electrode 68 and the second electrode 69 areisolated from each other by an isolation layer 600 b. The material ofthe isolation layer 600 b comprises dielectric material such as SiO₂ orSi₃N₄.

As shown in FIG. 6, the substrate 67 is a transparent substrate. A lightemitted from the active layer 62 can be emitted out through thetransparent substrate 67. The material of the substrate 67 can besapphire, glass, GaP, ZnSe, and SiC. The substrate 67 is attached to thefirst type semiconductor layer 63 by the bonding layer 65. The materialof the bonding layer 65 can be transparent material such as epoxy,polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB),spin-on glass (SOG) and silicone.

When the light-emitting device 6 is operated under a high electricalcurrent, the thickness of the buried electrode 64 is preferred to bethick with a range of about 2˜6 μm to reduce the sheet resistance of thelight-emitting device 6 and increase the device reliability. As shown inFIG. 6, when the light emitted from the active layer 62 passes throughthe bonding layer 65, part of the light is absorbed by the bonding layer65. In order to reduce the thickness H6 a of the bonding layer 65,improve the light emission efficiency of the light-emitting device 6,and maintain the thickness of the buried electrode 64 in a range ofabout 2˜6 μm, the plurality of buried electrodes 64 is buried in thefirst type semiconductor layer 63. The first type semiconductor layer 63comprises the top surface 63 a and a plurality of recesses 64 a. Each ofthe plurality of recesses 64 a comprises a bottom surface 64 b lowerthan the top surface 63 a of the first type semiconductor layer 63. Theconductive materials such as metal or metal alloy, or the transparentconductive materials such as ITO or ZnO are formed in the plurality ofrecesses 64 a to form the plurality of buried electrodes 64. Theconductive materials or the transparent conductive materials can beformed in the plurality of recesses 64 a by electron beam evaporation,physical vapor deposition or sputter deposition. The upper surface 64 cof each of the plurality of the buried electrodes 64 and the top surface63 a of the first type semiconductor layer 63 are substantially on thesame plane.

FIG. 7A illustrates an example of a cross-sectional diagram of theplurality of buried electrodes 64 in the light-emitting device 6according to the second embodiment of the present disclosure. As shownin FIG. 7A, the first type semiconductor layer 63 comprises the topsurface 63 a and the plurality of recesses 64 a. Each of the pluralityof recesses 64 a comprises the bottom surface 64 b lower than the topsurface 63 a of the first type semiconductor layer 63. The conductivematerials such as metal or metal alloy, and the transparent conductivematerials such as ITO or ZnO are formed in the plurality of recesses 64a to form the plurality of buried electrodes 64. The upper surface 64 cof each of the plurality of buried electrodes 64 and the top surface 63a of the first type semiconductor layer 63 are substantially on the sameplane.

As shown in FIG. 6, in order to increase the light emission efficiencyof the light-emitting device 6, the top surface 63 a of the first typesemiconductor layer 63 can be a non-planar surface as illustrated inFIG. 7B. FIG. 7B illustrates a cross-sectional diagram of the pluralityof buried electrodes 64 in the light-emitting device 6 according to thesecond embodiment of the present disclosure. As shown in FIG. 7B, thefirst type semiconductor layer 63 comprises the top surface 63 a and theplurality of recesses 64 a. The top surface 63 a is a non-planarsurface. The non-planar surface is a roughened surface 63 a′ and anaverage roughness of the roughened surface is greater than 0.05 μm. Thelight emission efficiency of the light-emitting device 6 is increased bythe roughened surface 63 a′. Each of the plurality of recesses 64 acomprises the bottom surface 64 b lower than the top surface 63 a of thefirst type semiconductor layer 63. The conductive materials such asmetal or metal alloy, and the transparent conductive materials such asITO or ZnO are formed in the plurality of recesses 64 a to form theplurality of buried electrodes 64. The upper surface 64 c of each of theplurality of the buried electrodes 64 is lower than the roughenedsurface 63 a′ of the first type semiconductor layer 63.

As shown in FIG. 6, the plurality of buried electrodes 64 is totallyburied in the first type semiconductor layer 63. The top surface 63 a ofthe first type semiconductor layer 63 and the upper surface 64 c of eachof the plurality of the buried electrode 64 are substantially on thesame plane. In the second embodiment illustrated in FIG. 6, theplurality of buried electrodes 64 is totally buried in the first typesemiconductor layer 63 and there is no exposed portion of each of theplurality of buried electrodes 64. Thus, the thickness H6 a of thebonding layer 65 used to attach the substrate 67 to the semiconductorstack 60 is reduced.

FIG. 8 illustrates a cross-sectional diagram of a light-emitting device8 according to the third embodiment of the present disclosure. Thelight-emitting device 8 comprises a substrate 87; a semiconductor stack80 comprising a first type semiconductor layer 83, a second typesemiconductor layer 81, and an active layer 82 formed between the firsttype semiconductor layer 83 and the second type semiconductor layer 81;a bonding layer 85 formed between the substrate 87 and the semiconductorstack 80; a first electrode 88 electrically connected to the first typesemiconductor layer 83; a second electrode 89 electrically connected tothe second type semiconductor layer 81; and a plurality of buriedelectrodes 84 physically buried in the first type semiconductor layer 83and electrically connected to the first electrode 88.

The material of the semiconductor stack 80 comprises III-V group basedsemiconductor material such as InGaN, AlGaAs, or AlGaInP. Thesemiconductor stack 80 is epitaxially grown on a growth substrate (notshown). The method of forming each layer of the semiconductor stack 80is not particularly limited. Besides a metal organic chemical vapordeposition method (MOCVD method), each layer of the semiconductor stack80 may be formed by a known method such as a molecular beam epitaxymethod (MBE method), a hydride vapor phase epitaxy method (HVPE method),a sputtering method, an ion-plating method and an electron showeringmethod.

The plurality of buried electrodes 84 buried in the first typesemiconductor layer 83 increases the contact area between the buriedelectrode 84 and the first type semiconductor layer 83. Each of theplurality of the buried electrode 84 electrically connected to eachother with an extension electrode (not shown). With the buried electrode84, the contact area between the buried electrode 84 and the first typesemiconductor layer 83 is increased and an electrical current isinjected into the first type semiconductor layer 83 uniformly.

A trench 800 is formed in the semiconductor stack 80 by etching process.A sidewall 800 a of the trench 800 is insulated from the semiconductorstack 80 with dielectric materials such as SiO₂ or Si₃N₄. A conductivechannel is formed by filling conductive material in the trench 800,wherein the conductive material can be metal or metal alloy, or atransparent conductive material like ITO or ZnO. The materials of theplurality of buried electrodes 84 and the first electrode 88 compriseconductive materials such as metal or metal alloy, and transparentconductive materials such as ITO or ZnO. The materials of the pluralityof buried electrodes 84, the first electrode 88 and the trench 800 arethe same or different from each other. The plurality of buriedelectrodes 84 and the first electrode 88 are electrically connected viathe conductive channel. The first electrode 88 and the second electrode89 are formed on the same side of the semiconductor stack 80 opposite toa top surface 83 a of the first type semiconductor 83. The firstelectrode 88 and the second electrode 89 are isolated from each other byan isolation layer 800 b. The material of the isolation layer 800 bcomprises dielectric material such as SiO₂ or Si₃N₄.

As shown in FIG. 8, the substrate 87 is a transparent substrate. A lightemitted from the active layer 82 can be emitted out through thetransparent substrate 87. The material of the substrate 87 can besapphire, glass, GaP, ZnSe, and SiC. The substrate 87 is attached to thefirst type semiconductor layer 83 by the bonding layer 85. The materialof the bonding layer 85 can be transparent material such as epoxy,polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB),spin-on glass (SOG) and silicone.

When the light-emitting device 8 is operated under a high electricalcurrent, the thickness of the buried electrode 84 is preferred to bethick with a range of about 2˜6 μm to reduce the sheet resistance of thelight-emitting device 8 and increase the device reliability. As shown inFIG. 8, when the light emitted from the active layer 82 passes throughthe bonding layer 85, part of the light is absorbed by the bonding layer85. In order to reduce the thickness H8 a of the bonding layer 85,improve the light emission efficiency of the light-emitting device 8,and maintain the thickness of the buried electrode 84 in a range ofabout 2˜6 μm, the plurality of buried electrodes 84 is buried in thefirst type semiconductor layer 83. The first type semiconductor layer 83comprises the top surface 83 a and a plurality of recesses 84 a. Each ofthe plurality of recesses 84 a comprises a bottom surface 84 b lowerthan the top surface 83 a of the first type semiconductor layer 83. Theconductive materials such as metal or metal alloy, or the transparentconductive materials such as ITO or ZnO are formed in the plurality ofrecesses 84 a to form the plurality of buried electrodes 84. Theconductive materials or the transparent conductive materials can beformed in the plurality of recesses 84 a by electron beam evaporation,physical vapor deposition or sputter deposition. The upper surface 84 cof the buried electrode 84 is lower than the top surface 83 a of thefirst type semiconductor layer 83.

The plurality of buried electrodes 84 is buried in the first typesemiconductor layer 83. FIG. 9A illustrates a cross-sectional diagram ofthe plurality of buried electrodes 84 in the light-emitting device 8according to the third embodiment of the present disclosure. As shown inFIG. 9A, the first type semiconductor layer 83 comprises the top surface83 a and the plurality of recesses 84 a. Each of the plurality ofrecesses 84 a comprises the bottom surface 84 b lower than the topsurface 83 a of the first type semiconductor layer 83. The conductivematerials such as metal or metal alloy, and the transparent conductivematerials such as ITO or ZnO are formed in the plurality of recesses 84a to form the plurality of buried electrodes 84. The upper surface 84 cof the buried electrode 84 is lower than the top surface 83 a of thefirst type semiconductor layer 83.

As shown in FIG. 8, in order to increase the light emission efficiencyof the light-emitting device 8, the top surface 83 a of the first typesemiconductor layer 83 can be a non-planar surface as illustrated inFIG. 9B. FIG. 9B illustrates a cross-sectional diagram of the pluralityof buried electrodes 84 in the light-emitting device 8 according to thethird embodiment of the present disclosure. As shown in FIG. 9B, thefirst type semiconductor layer 83 comprises the top surface 83 a and theplurality of recesses 84 a. The top surface 83 a is a non-planarsurface. The non-planar surface is a roughened surface 83 a′ and anaverage roughness of the roughened surface 83 a′ is greater than 0.05μm. The light emission efficiency of the light-emitting device 8 isincreased by the roughened surface 83 a′. Each of the plurality ofrecesses 84 a comprises the bottom surface 84 b lower than the topsurface 83 a of the first type semiconductor layer 83. The conductivematerials such as metal or metal alloy, and the transparent conductivematerials such as ITO or ZnO are formed in the plurality of recesses 84a to form the plurality of buried electrodes 84. The upper surface 84 cof each of the plurality of the buried electrode 84 is lower than theroughened surface 83 a′ of the first type semiconductor layer 83.

As shown in FIG. 8, the plurality of buried electrodes 84 is totallyburied in the first type semiconductor layer 83. The upper surface 84 cof the buried electrode 84 is lower than the top surface 83 a of thefirst type semiconductor layer 83. In the third embodiment illustratedin FIG. 8, the plurality of buried electrodes 84 is totally buried inthe first type semiconductor layer 83 and there is no exposed portion ofeach of the plurality of buried electrodes 84. Thus, the thickness H8 aof the bonding layer 85 used to attach the substrate 87 to thesemiconductor stack 80 is reduced.

The principle and the efficiency of the present disclosure illustratedby the embodiments above are not the limitation of the disclosure. Anyperson having ordinary skill in the art can modify or change theaforementioned embodiments. Therefore, the protection range of therights in the disclosure will be listed as the following claims.

What is claimed is:
 1. A light-emitting device, comprising: a substrate;a semiconductor stack comprising a first type semiconductor layer, asecond type semiconductor layer and an active layer formed between thefirst type semiconductor layer and the second type semiconductor layer,wherein the first type semiconductor layer comprises a non-planarroughened surface; a bonding layer formed between the substrate and thesemiconductor stack; and multiple recesses each comprising a bottomsurface lower than the non-planar roughened surface; and multiple buriedelectrodes physically buried in the first type semiconductor layer,wherein the multiple buried electrodes are formed in the multiplerecesses respectively, and one of the multiple buried electrodescomprises an upper surface higher than the non-planar roughened surfaceof the first type semiconductor layer.
 2. The light-emitting deviceaccording to claim 1, wherein one of the multiple buried electrodescomprises an embedded portion under the non-planar roughened surface ofthe first type semiconductor layer and an exposed portion above thenon-planar roughened surface of the first type semiconductor layer. 3.The light-emitting device according to claim 2, wherein the size of theembedded portion is larger than that of the exposed portion.
 4. Thelight-emitting device according to claim 2, wherein the embedded portionis electrically connected to the semiconductor stack.
 5. Thelight-emitting device according to claim 1, wherein an average roughnessof the non-planar roughened surface is greater than 0.05 μm.
 6. Thelight-emitting device according to claim 1, wherein one of the multipleburied electrodes comprises metal or metal alloy.
 7. The light-emittingdevice according to claim 1, wherein the bottom surface is planar. 8.The light-emitting device according to claim 1, wherein a thickness ofone of the multiple buried electrode is in a range of about 2˜6 μm. 9.The light-emitting device according to claim 1, wherein the material ofthe semiconductor stack comprises InGaN, AlGaAs, or AlGaInP.
 10. Alight-emitting device, comprising: a substrate; a semiconductor stackcomprising a first type semiconductor layer, a second type semiconductorlayer and an active layer formed between the first type semiconductorlayer and the second type semiconductor layer wherein the first typesemiconductor layer comprises a top surface; a bonding layer formedbetween the substrate and the semiconductor stack; multiple recessesrecessed from the top surface toward the active layer; and multipleburied electrodes in the multiple recesses respectively, wherein anupper surface of one of the multiple buried electrodes is higher thanthe top surface of the first type semiconductor layer.
 11. Thelight-emitting device according to claim 10, wherein one of the multiplerecesses comprises a bottom surface lower than the top surface of thefirst type semiconductor layer, and the bottom surface is planar. 12.The light-emitting device according to claim 10, wherein one of themultiple buried electrodes comprises an embedded portion fully embeddedin one of the multiple recesses and an exposed portion protruded out ofthe top surface of the first type semiconductor layer.
 13. Thelight-emitting device according to claim 12, wherein the size of theembedded portion is larger than that of the exposed portion.
 14. Thelight-emitting device according to claim 12, wherein the embeddedportion is electrically connected to the semiconductor stack.
 15. Thelight-emitting device according to claim 10, wherein the top surface ofthe first type semiconductor layer is a roughened surface.
 16. Thelight-emitting device according to claim 15, wherein an averageroughness of the roughened surface is greater than 0.05 μm.
 17. Thelight-emitting device according to claim 10, wherein one of the multipleburied electrodes comprises metal or metal alloy.
 18. The light-emittingdevice according to claim 10, wherein the thickness of one of themultiple buried electrode is in a range of about 2˜6 μm.
 19. Thelight-emitting device according to claim 10, wherein the material of thesemiconductor stack comprises InGaN, AlGaAs, or AlGaInP.